1. Field of the Invention
The invention relates to the field of configuring lines of complex industrial robots, especially the so-called pick and place machines, using incomplete search techniques.
2. Related Art
The invention is an improvement on U.S. Pat. No. 5,390,283 (xe2x80x9c283xe2x80x9d) and U.S. Pat. No. 5,864,833 (xe2x80x9c833xe2x80x9d), both of which are incorporated herein by reference.
Multiple head pick and place machines present a nearly intractable combinatorial problem, because there are so many layout optionsxe2x80x94what with multiple pickup nozzles, pipette modules, gripper types, feeders, trays, and so forth. It is desirable to choose the proper combination of options, so that part placement is conducted as quickly as possible, but searching all the options is impractical. Accordingly, an incomplete search of the space of layouts is undertaken.
""283 teaches creating a layout, a.k.a. configuration, for a single pick and place machine using an incomplete search technique known as a genetic algorithm (xe2x80x9cGAxe2x80x9d) in combination with a heuristic layout generator (xe2x80x9cHLGxe2x80x9d) to generate the layout. A form of GA known as CHC is preferred. The GA uses a population of chromosome strings, each containing genes that influence the HLG. The GA crosses over and mutates the population, and causes elimination of unfit individuals, in a simulation of the biological process of evolution. The HLG attempts to translate each chromosome string into an actual layout and then evaluates how good that layout or partial layout is. The quality assessment by the HLG is used in each subsequent iteration of the GA to determine which chromosome strings live or die.
The GA is a technique that generally requires a great deal of experimentation to apply to a particular problem. A chromosome string format representing a problem solution needs to be developed. Then the format must be tested by multiple applications of the GA, testing the results each time, to see if the format repeatedly results in convergence towards an improved solution. Typically several string formats must be tested prior to selection of a preferred one. It is not usually possible to predict what format will work for a given problem, especially if that problem is not simple.
""833 refines the techniques of ""283 for lines of at least two pick and place machines of different types. ""833 adopts a chromosome string which represents a unified layout for the entire line and then uses a GA and an HLG to find layout solutions for the line. ""833""s preferred embodiment shows a line of two machines of different types, a Philips FCM and a Philips ACM.
The object of the present invention is to improve the techniques of ""833.
This object is achieved by modularizing the chromosome string and the HLG. In particular, the allocation of part types to machine types is carried out in a separate step from the rest of the layout generation.